1. Field of the Invention
This invention relates generally to telescoping strut constructions, and more particularly to safety-lock structures associated therewith, which tend to avoid accidental or inadvertent release while the strut is under load.
2. Description of the Related Art Including Information Disclosed Under 37 CFR Sections 1.97-1.99
The following prior art references are hereby cited as being of interest in the field to which the present invention pertains:
______________________________________ U.S. Pat. Nos.: ______________________________________ 3,367,689 3,390,874 3,442,541 3,469,871 3,945,744 4,014,467 4,362,415 4,366,945 4,453,449 4,453,748 4,546,956 4,682,795 4,960,344 5,066,049 5,265,970 ______________________________________
U.S. Pat. No. 3,442,541 discloses a telescoping strut construction having inner and outer members, and a locking sleeve that is carried on one of the members and which is shiftable axially on the one member between locking and unlocking positions, to effect either a lock or a release of the members with respect to one another. In accomplishing the locking function, the inner member is engaged by locking dogs carried respectively in radial slots in the outer member. The inner member has transverse locking ribs which fit into corresponding locking ribs on the dogs. In a locked condition of the strut, the dogs are held in forcible engagement with the ribs on the inner member. Release of the strut is accomplished by manually shifting the locking sleeve, to a position wherein the locking dogs can shift outwardly in response to axial force applied between the members.
U.S. Pat. No. 3,469,871 shows a lockable coupling having telescoping inner and outer members and which employs two arcuate locking dogs carried in a circumferential groove of the inner member, and also utilizes a multiplicity of force-transmitting balls housed in radial slots of the inner member. Each locking dog is engaged by two balls. In operation, a release member or rod having a conical actuator portion engages the balls and shifts them radially, along with the arcuate locking dogs. During locking, the dogs are shifted laterally into inner annular grooves on the outer telescoping member. Locking and release of the telescoping members is accomplished by axially displacing a release member, by means of a pin-coupled release collar (64, FIG. 2) carried by the inner telescoping member.
Other constructions involving struts of the type employing radially shiftable locking components are illustrated in U.S. Pat. No. 3,390,874, and U.S. Pat. No. 3,367,689.
U.S. Pat. No. 4,362,415 illustrates a locking strut having a slidable locking collar which can be positively retained in a locking position by an external spring-biased locking lever.
U.S. Pat. No. 4,546,956 discloses a releaseable coupling for a hose that is attachable to a container of compressed gas. The arrangement is such that the coupling cannot be removed from the supply fitting until after the pressure in the container is reduced, to minimize the danger to personnel from an inadvertent, gas-propelled "fly off" of the coupling. Although the device provides a safety interlock feature, it is not a strut, and the structure and mode of operation of the device is different from that of the present invention, as will be apparent hereinbelow.
U.S. Pat. Nos. 4,014,467; 4,366,945; 4,453,748; 4,682,795; and 5,066,049 all involve releasable hose fittings/couplings having various types of locking structures that employ captive balls.
U.S. Pat. No. 4,960,344 discloses a coupling between a drive shaft and a driven shaft of a tractor. U.S. Pat. No. 4,453,449 relates to a re-useable, non-destructive hold-down apparatus employing locking balls, which apparatus grips a member such as a missile or projectile until a certain propulsion force is developed by the same, and which thereafter releases the member suddenly.
In connection with most prior struts, there have existed significant problems involving inadvertent release under load. Specifically, with either compressive or tensile loads applied between the telescoping members of the prior art struts, there was a danger that the operator could slide the locking collar to a release position while the strut was still under load, possibly leading to a sudden collapse of the strut and an accompanying uncontrollable swing or fall of the component being held, by virtue of its own weight. Such a condition was capable of causing serious injury to either the operator or to other personnel in the area.
In the past, struts of the type noted have been used with aircraft cowlings, in order to retain the cowlings in an open position as during maintenance, and/or servicing of the aircraft engines. Depending on the size of the aircraft, such cowlings can weight hundreds of pounds, and the potential of injury resulting from being struck by an inadvertently released cowling can be readily appreciated if one considers structures of such magnitude and size.
One solution to the problem of inadvertent release of a strut is set forth in U.S. Pat. No. 5,265,970 having common ownership with the present invention. FIGS. 6-9 of this patent illustrate the general concept involved, namely one of preliminary release of the load from the strut before an unlocking sleeve can be activated or shifted toward a release position. In particular, the load which normally existed between the extended inner and outer members of the strut while under compression also applied a locking force to the axially-slidable locking sleeve on one of the members. With load applied, not only were the members locked to each other, but the locking sleeve was locked to one member.
In order to effect release of the telescoping members, it was first necessary to remove the compressive load that the members were supporting. Thereafter, the members had to be manually extended by a slight amount, past their normal, extended, compressive load-bearing positions. With the members being held manually in such an over-extended position, they in effect freed the locking elements for the telescoping members from forcible engagement with the locking sleeve, enabling the latter to be thereby manually shifted axially so as to bring a relieved area on the inner surface of the sleeve into registration with the locking elements. As the strut members were subsequently retracted from this over-extended position, the locking elements were shifted into the relieved area of the sleeve and remained there as the collapsing movement continued. A full collapse of the strut could then be accomplished.
Because of the necessity to deliberately remove the load first, prior to moving the strut members at all, a good degree of control over the operation of the strut and its load was achievable, which contributed to the safety of the overall installation, as regards maintenance personnel and equipment.
With the advent of still larger and heavier aircraft having correspondingly larger cowlings, the need arises for longer and stronger safe compressive struts for such cowlings, based on the proven principles of the above-identified patent.